- Determining the Fate of a Non-Heme Iron Oxidation Catalyst Under Illumination, Oxygen, and Acid
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We analyze the stability of the non-heme water oxidation catalyst (WOC), Fe(bpmcn)Cl2 toward oxygen and illumination under nonaqueous and acidic conditions. Fe(bpmcn)Cl2 has been previously used as a C-H activation catalyst, a homogeneous WOC, and as a cocatalyst anchored to WO3 for photoelectrochemical water oxidation. This paper reports that the ligand dissociates at pH 1 with a rate constant k = 19.8(2) × 10-3 min-1, resulting in loss of catalytic activity. The combination of UV-vis experiments, 1H NMR spectroscopy, and cyclic voltammetry confirm free bpmcn and Fe2+ present in solution under acidic conditions. Even under nonaqueous conditions, both oxygen and illumination together show slow oxidation of iron over the course of a few hours, consistent with forming an Fe3+-O2- intermediate as corroborated by resonance-enhanced Raman spectroscopy, with a rate constant of k = 3.03(8) × 10-3 min-1. This finding has implications in both the merits of non-heme iron complexes as WOCs as well as cocatalysts in photoelectrochemical schemes: the decomposition mechanisms may include both anchoring group hydrolysis and instability under illumination.
- Esarey, Samuel L.,Holland, Joel C.,Bartlett, Bart M.
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- Synthesis of water-soluble Ni(II) complexes and their role in photo-induced electron transfer with MPA-CdTe quantum dots
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Abstract: Photocatalytic water splitting using solar energy for hydrogen production offers a promising alternative form of storable and clean energy for the future. To design an artificial photosynthesis system that is cost-effective and scalable, earth a
- Botcha, Niharika Krishna,Gutha, Rithvik R.,Sadeghi, Seyed M.,Mukherjee, Anusree
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p. 143 - 153
(2019/09/10)
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- Catalytic oxidation of alcohols with novel non-heme N4-tetradentate manganese(ii) complexes
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We report the preparation and characterisation of a series of novel non-heme N4-tetradentate Mn(OTf)2 complexes of the type, [(L)MnOTf2], where L = R,R and S,S enantiomers of BPMCN, its 6-methyl and 6-bromo derivatives as well as the novel ligand BMIMCN (BPMCN = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)-(R,R/S,S)-1,2-diaminocyclohexane, BMIMCN = N,N′-dimethyl-N,N′-bis(1-methyl-2-imidazolemethyl)-(R,R/S,S)-1,2-diaminocyclohexane). Solid state structural analysis of the BMIMCN-ligated Mn-triflate complexes (R,R-C4 and S,S-C4) revealed opposite helicity but identical metal site accessibility. This feature was exploited in the catalytic oxidation of primary and secondary alcohols, with hydrogen peroxide as oxidant and acetic acid as co-catalyst. Complexes R,R-C4 and S,S-C4 displayed the highest activity in benzyl alcohol oxidation, attributed to the electron-donating property of the BMIMCN ligand. Complex S,S-C4, displayed high activity for a variety of primary alcohol substrates, but the reaction suffered from reduced selectivity and side-reactions due to the presence of acetic acid. In contrast, secondary alcohol substrates could be oxidised to the corresponding ketone products in excellent isolated yields under mild reaction conditions and short reaction times.
- Vermaak, Vincent,Young, Desmond A.,Swarts, Andrew J.
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supporting information
p. 16534 - 16542
(2018/12/05)
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- The iron(II) complex [Fe(CF3SO3)2(mcp)] as a convenient, readily available catalyst for the selective oxidation of methylenic sites in alkanes
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The efficient and selective oxidation of secondary C-H sites of alkanes is achieved by using low catalyst loadings of a non-expensive, readily available iron catalyst [Fe(II)(CF3SO3)2(mcp)], {Fe-mcp, [mcp=N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)cyclohexane-trans-1,2-diamine]}, and hydrogen peroxide (H2O2) as oxidant, via a simple reaction protocol. Natural products are selectively oxidized and isolated in synthetically amenable yields. The easy access to large quantities of the catalyst and the simplicity of the C-H oxidation procedure make this system a particularly convenient tool to carry out alkane C-H oxidation reactions on the preparative scale, and in short reaction times.
- Canta, Merce,Font, David,Gomez, Laura,Ribas, Xavi,Costas, Miquel
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p. 818 - 830
(2014/04/03)
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- Manganese complexes with non-porphyrin N4 ligands as recyclable catalyst for the asymmetric epoxidation of olefins
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New chiral manganese complexes of N4 ligands derived from 2-acetylpyridine were prepared and used as catalysts in the enantioselective epoxidation of olefins, using H2O2 as an oxidant to give epoxides, with excellent conversions (up to 99%) and enantiomeric excess (up to 88%) within 1 h at 0°C. A detailed mechanistic study was undertaken based on the information obtained by single crystal X-ray, optical rotation, UV-Vis, CD spectra and kinetic studies, and revealed that the reaction is first order with respect to the concentration of catalyst and oxidant and independent of substrate concentration. The complex (0.1 mol%) was successfully subjected to recyclability experiments over 3 cycles in the epoxidation of styrene with H2O2 as an oxidant and acetic acid as an additive at 0°C with retention of performance.
- Maity, Nabin Ch.,Kumar Bera, Prasanta,Ghosh, Debashis,Abdi, Sayed H. R.,Kureshy, Rukhsana I.,Khan, Noor-Ul H.,Bajaj, Hari C.,Suresh
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p. 208 - 217
(2014/01/06)
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- Iron coordination chemistry of N2Py2 ligands substituted by carboxylic moieties and their impact on alkene oxidation catalysis
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A biomimetic approach based on Rieske dioxygenase mimics has been undertaken, which uses the tetradentate N2Py2 ligand platform that contains two pyridine moieties linked to a 1,2-diaminoethane or a trans-1,2-diaminocyclohexane backb
- Oddon, Frederic,Girgenti, Elodie,Lebrun, Colette,Marchi-Delapierre, Caroline,Pecaut, Jacques,Menage, Stephane
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experimental part
p. 85 - 96
(2012/03/13)
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